This invention relates to an antenna device for controlling a direction of a radio wave.
An antenna device of the type described is for use in transmitting or receiving a radio wave in an earth station for carrying out communication in a satellite communication system through a satellite. The earth station is often carried on an automobile and is therefore movable on the earth, communicating with the satellite. In this case, such a movable earth station must always follow or trace the satellite. Otherwise, communication is undesirably interrupted between the movable earth station and the satellite. To this end, the conventional antenna section comprises an antenna block mechanically driven to orient a radio wave towards the satellite. However, it is difficult to quickly trace the satellite by mechanically driving the antenna block because the movable earth station moves fast.
In order to quickly control the direction of the radio wave, an improved antenna device is disclosed on pages 270 to 287 of a book "Microstrip Antennas" written by I. J. Bahl and P. Bhartia and published 1979 by ARTECH HOUSE. In the improved antenna device, an antenna block is formed by an antenna section and a control section. The antenna section has a plurality of antenna elements which are spaced apart by a predetermined distance and which are driven in parallel while the control section is connected to the antenna section to electrically control the antenna section to electrically change the direction of the radio wave. The control section comprises a plurality of phase shifters connected to the antenna elements to individually phase shift input signals, respectively. As a result, the phase shifters produce phase shifted signals in accordance with phase shifts or phase shift values different from one another so as to electrically control the direction of the radio wave.
However, the phase shifters must be manufactured with a desired precision so as to realize desired phase shifts in the phase shifters. In general, it is very difficult to manufacture such phase shifters with the desired precision. Accordingly, some mechanical error is inevitable in the phase shifters. If phase differences between the phase shifts or phase shift values are different from the designed phase shifts in the phase shifters, noise takes place in a reception signal or a transmission signal due to the phase differences.